Dewaxing is a commonly used technique for improving the properties of a petroleum fraction for use in various products, such as fuels or lubricant base stocks. Historically, solvent dewaxing was the first type of dewaxing used for modifying the properties of a feedstock. Solvent extraction and dewaxing allowed for separation of a feedstock into a raffinate fraction for use as a distillate fuel or lubricant, an aromatics fraction, and a waxy fraction. More recently, catalytic dewaxing has been commonly used for improving the properties of feeds for use in fuels or lubricant base stocks.
U.S. Pat. No. 4,259,170 describes a process for manufacturing lube basestocks. In the process, one or more lower boiling fractions from a vacuum distillation tower are solvent dewaxed to form lubricant base stocks. One or more higher boiling fractions are catalytically dewaxed in order to provide a pour point improvement for the higher boiling fractions that is greater than the amount that can be achieved by solvent dewaxing.
U.S. Pat. No. 6,773,578 describes a process for preparing lubes with high viscosity index values. The process includes obtaining a first feedstock that includes at least 95% of material that boils below 1150° F. (621° C.), and a second feedstock that includes at least 95% of material that boils above 1150° F. (621° C.). The feedstock containing the portion that boils below 1150° F. is catalytically dewaxed. The feedstock containing the portion that boils above 1150° F. is solvent dewaxed and optionally also catalytically dewaxed. Performing solvent dewaxing on the above 1150° F. portion is described as reducing the difference between the cloud point and the pour point for the resulting products.
U.S. Pat. No. 7,354,508 describes a process for preparing a heavy and a light lubricating base oil. A feedstock for forming lubricant basestocks is separated into a lower boiling fraction and a higher boiling fraction. The lower boiling fraction and higher boiling fraction are dewaxed under different conditions. Solvent dewaxing is generally mentioned as a type of dewaxing. However, catalytic dewaxing is identified as the preferred type of dewaxing for dewaxing of both fractions.